Introduction: Sexually transmitted diseases (STUD) are a significant public health problem, especially among adolescents. In order to plan effective interventions for adolescents, longitudinal studies need to be conducted that will aid in the understanding of the psychological and behavioral issues that underlie the initial STD acquisition as well as the responses of the adolescent following acquisition. Aims: The first aim is to examine the complex relationships of the components of adolescent development to adolescent girl's sexual behavior and the consequences of sexual behavior on adolescent girls. Components of adolescent development include: cognitive, psychosexual, and biological maturation, knowledge and perceptions, sociocultural context, and the adolescent's ability to manage situations. The second aim is to examine, longitudinally, the relationship of the developmental changes in psychological development and sexual practices for adolescent girls. This aim will examine changes in adolescents' beliefs and behaviors after they acquire or do not acquire an STD. Methods: One hundred and seventy-five adolescent girls, ages 12-15, will be recruited from their source of primary care in an urban adolescent clinic. The sample will consist of a racially mixed cohort, with both sexually inexperienced and experienced girls. They will be evaluated every 6 months for three years. At each 6-month visit, psychological/behavioral data will be collected by interview and standardized assessment measures. The sexually experienced subjects will receive a pelvic exam and Pap smear, and standard procedures will be used for the diagnosis of trichomonas, gonorrhea, and Chlamydia infections. Once yearly, a polymerase chain reaction assay for human papillomavirus will be performed and blood will be obtained for syphilis serology and herpes simplex virus serotyping. Confidential testing for human immunodeficiency virus will occur at the beginning and the end of the study. Subjects with positive results will be referred to their primary care provider. Medical charts will be reviewed to document any STD that occurs between study appointments. Clinical Significance: Behavioral/psychological strategies will continue to be the fundamental approach to the prevention of sexually transmitted diseases in adolescents. This longitudinal study will provide data regarding adolescent development across the adolescent age span and levels of sexual experience. The adolescent's style of coping as it relates to her perception of sexually transmitted diseases will be characterized. This study will improve our understanding of adolescents who place themselves at risk for sexually transmitted diseases.